From: Dictionary of American Naval Fighting Ships, Vol.VI p 165

Ruby

Red extremely hard crystal of aluminum oxide used as a precious stone.

Patrol craft Ruby (PY-21), formerly Placida, was built as a diesel motor yacht in 1930 by Bath Iron Works, Bath, Maine; purchased by the Navy from H. G. Haskell 19 June 1941 ; converted to a patrol vessel at Gibbs Gas Engine Co., Jacksonville, Fla, ; commissioned 23 September 1941 ; and assigned to the 6th Naval District at Charleston, S.C., for escort duty.

From 10 February 1942 to 18 January 1944 Ruby was assigned to the Eastern Sea Frontier, retaining her homeport of Charleston. On the 18th she was reassigned to the 3d Naval District at New York, and 3 days later was given to the 1st Naval District at Boston for training purposes.

Ruby decommissioned at Boston 25 July 1945, was struck from the Navy list 13 August 1945, and transferred to the Maritime Commission 26 December.